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Date: Wed, 22 Jun 2005 22:05:54 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Bill Huey <bhuey@lnxw.com>
Cc: Karim Yaghmour <karim@opersys.com>, Kristian Benoit <kbenoit@opersys.com>,
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Subject: Re: PREEMPT_RT vs I-PIPE: the numbers, part 2
Message-ID: <20050622200554.GA16119@elte.hu>
References: <1119287612.6863.1.camel@localhost> <20050620183115.GA27028@nietzsche.lynx.com> <42B98B20.7020304@opersys.com> <20050622192927.GA13817@nietzsche.lynx.com>
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* Bill Huey <bhuey@lnxw.com> wrote:

> > target is subject to the HD test. For a pipe, this goes from 9.4us
> > to 21.6. For UDP this goes from 22us to 1070us !!! Even on a
> > system without any load, the numbers are similar. Ouch.
> 
> I'm involved in other things now, but I wouldn't be surprised if it 
> was some kind of scheduler bug + softirq wacked interaction. [...]

the UDP-over-localhost latency was a softirq processing bug that is 
fixed in current PREEMPT_RT patches. (real over-the-network latency was 
never impacted, that's why it wasnt noticed before.)

	Ingo